1. Field of the Invention
This invention relates to a laminated LC element, and particularly to a distributed constant type laminated LC element for making up a distributed constant circuit for an LC which includes inductance conductors and capacitor conductors in a laminate having a number of insulating layers.
2. Description of the Related Art
Along with the recent development of the electronics technology, electronic circuits have been widely applied to a variety of fields. It has been strongly demanded that those electronic circuits function stably and properly without being affected by external noises.
In addition, various sophisticated electronic devices have been widely used at present, and the demand for strict noise reduction has increased accordingly. So as to satisfy such demand, it has been desired to develop noise filters which can eliminate the noises sufficiently, and are compact and has a high quality.
As shown in FIG. 21 of the accompanying drawings, a conventional LC noise filter comprises a pair of windings 12, 14 wound around a core 10, and capacitors 16, 18 connected in parallel to both ends of the windings 12, 14.
The core 10 and windings 12, 14 composing an inductor are bulky, and the inductor and capacitor 16, 18 are separate members. Therefore the filter becomes large and cannot satisfy the demand for compact size and light weight.
Various proposals have been made to cope with the above-mentioned problems as disclosed in Japanese Patent Laid-Open Publications 50507/1981, 144524/1981, 142622/1981, and 76313/1988.
For example, Japanese Patent Laid-Open Publication No. 50507/1981 discloses compound electronic parts, in which a laminate is composed by disposing a plurality of insulating layers 20a, 20b, 20c, ... as shown in FIGS. 22(a) to 22(f). In addition, conductor patterns 22a, 22b, 22c are disposed around the insulating layers 20a, 20b, ... so as to compose a coil having the predetermined number of turns.
Conductive layers 24a, 24b are disposed between the insulating layers 20a, 20b, 20c, ... apart from the conductor patterns 22a, 22b, thereby providing a capacitance C between the conductive layers 24a, 24b and the conductor patterns 22a, 22b. Thus a concentrated constant type noise filter having L and C is obtained as shown in FIG. 23.
The LC noise filter of the conventional example is compact in size and light weight since L and C are built in the layers. However this filter has some inconveniences in the following: (1) the conductive layers 24a, 24b providing a capacitance are simply disposed adjacent to the straight portion of the conductor patterns 22a, 22c serving as a coil. Therefore the capacitance C between the coil and the conductive layers 24 is too small to offer a good attenuation. In addition, since the LC filter of FIG. 23 is of the concentrated constant type, it cannot sufficiently remove various noises, particularly common mode noises such as switching surge, and normal mode noises such as ripples. (2) Further, the LC filter can be used as a 3-terminal type normal mode filter but not as a 4-terminal type common mode filter.